This invention relates generally to medical devices, and in particular, to medical retrieval devices for engaging and/or removing objects, such as calculi and the like, from the body.
Various organs and passages in the body are subject to the development of stones, calculi and the like. Gallstones are a common problem in the United States and are the most frequent cause of gallbladder inflammation. Calculi in other parts of the biliary system are also commonplace. Similarly, stones, calculi and the like can develop throughout the renal or urinary system, not only in the ureters and distal to them, but also in the renal tubules and in the major and minor renal calyxes. The calyxes are hollow collecting structures in the kidneys, extending from the renal pelvis, the minor calyxes in particular joining the renal pyramids. For simplicity, the calyxes can be considered as ducts extending from the connecting tubules of the renal nephrons to the ureters.
Minimally invasive surgical procedures have been developed for the removal of stones, calculi and the like from the biliary and urinary systems. Such procedures avoid the performance of invasive, open surgical procedures (such as, for example, the cholecystectomy) and can instead employ percutaneous access, in which stones, calculi and the like are removed through a percutaneously inserted access sheath. Several access routes are suitable, depending upon the specific system and the particular location in the system at which the stones, calculi or the like are found. Without regard to the access route, however, percutaneous removal is usually based upon the use of either forceps or basket-tipped catheters to engage and remove the stones, calculi, and the like.
A closed, wire tipped basket (helical or straight wire) permits entry of the stone or the like from the side of the basket, while an open ended basket allows a head-on approach to the stone or the like. Other retrievers and graspers can include forceps or can include a loop or snare for encircling the body to be removed, the loop or snare being made of, for example, round or flat wire. Flat wire has the advantage over round wire in that baskets incorporating flat wire exhibit better resistance to twisting during use. Moreover, while surgical techniques have advanced, and endoscope accessory channels of a relatively smaller diameter have been developed, efforts to reduce the diameter of round wires incorporated in stone extraction baskets have unfortunately not met with similar success. In practice, the lowest useful round wire diameter remains about 0.007 to 0.010 in. (about 0.178 to 0.254 mm). Because there is a significant amount of wasted space inside any sheath or cannula containing round or flat wires, this limit on useful wire diameter has prevented the development of useful stone extractors of small diameter, and in particular, of extractors having an outside diameter (that is, the diameter of the sheath or cannula containing the wires) below about 1.7 French (0.022 in. or 0.56 mm).
Another desirable feature of smaller retrieval devices, especially important for urological use, would be to have a device that works with a small diameter endoscope, such as an ureteroscope, that is capable of accommodating accessory instrumentation such as a laser fiber or hydraulic lithotripsy wire to break up stones or calculi for easier removal. The limited space and limited numbers of lumens available in the smaller scopes makes it advantageous to create devices that are capable of sharing the existing accessory channels of the endoscope without having to increase lumen diameter. While some small-diameter retrieval devices are capable of being introduced through a ureteroscope, the size and design of the wire precludes having an internal lumen through which accessory instrumentation, such that for performing a lithotripsy procedure, can be introduced into the workspace of the retrieval device.
The foregoing problems are solved and a technical advance is achieved in an illustrative medical retrieval device which is particularly useful with an endoscope for engaging or capturing and removing, extracting, or retrieving objects such as stones, calculi, concretions, foreign bodies and the like from a variety of locations in the body. The disclosed embodiments of the present medical retrieval device can each be characterized as being formed from a single elongated member wherein the resilient grasping members of the distal portion of the elongated member each represent a continuum of a material that essentially extends the length of the device. The resilient members form either a basket or a forceps.
In one embodiment of the present invention, the individual grasping members result from longitudinally slotting the elongated member about one end. The elongated member can be a hollow cannula or a solid member, preferably cylindrical in shape. The slots are formed by removing material of the elongated member in the form of longitudinal, elongated slots. The resilient grasping members result about the circumference of the elongated member with the remaining material thereof. Alternatively, the members result from the removal of material to expose elements, such as reinforcement wires, that are already encased within the walls of the elongated member. Advantageously, the members can comprise a basket or snare when the grasping members are interconnected at the distal end of the device, or grasping forceps when they are not.
Basket-making methodology has previously involved soldering, welding, crimping, or otherwise attaching the basket wires to a separate shaft piece. By having the wires or resilient grasping members being continuous with the proximal shaft portion of the device, any joint is advantageously eliminated. Such a joint can be more subject to breakage, possibly resulting in the dangerous situation of having a loose broken wire within the patient. Another advantage of a retrieval basket, grasper, or forceps of the present invention made from a thin-walled cannula or tube is the large open lumen and a small relative O.D. This large open lumen advantageously permits lithotripsy procedures to be performed when the retrieval device is inserted through an utereoscope. The present invention is particularly advantageous over the prior art in that the device can have an overall outside diameter significantly smaller than the outside diameter of existing retrieval or extraction devices, wherein the joint between wires and shaft increases the outer diameter and/or the available inner lumen diameter. The retrieval device of the present invention can have an outside diameter as small as 1 Fr., although 2-3 French is a preferred size for use in conjunction with a ureteroscope and laser fiber or lithotripsy laser fiber. Smaller devices will be able to reach deeper inside the body to capture and retrieve stones and calculi. It should go without saying that the smaller diameter is also expected to reduce the risk of patient discomfort and the risk of inadvertent damage to tissue during introduction and manipulation of the device in the patient.
Visualization of the target object is essential when using a retrieval device. Endoscopes, used in most minimally invasive procedures to retrieve stones or calculi, typically have a second or third accessory channel or lumen for introducing ancillary devices to the treatment site. The smaller diameter endoscopes, such as a ureteroscope, have a very narrow accessory channel through which the retrieval device is fed. An advantage of the present invention is that the tubular design, with its large central lumen, allows the introduction of additional instrumentation useful to the procedure such as a guidewire that may be used for placement, or a device to break up a stone or calculus such as a laser fiber or electrohydraulic lithotripsy wire. Conventional basket or grasper forceps manufacturing techniques that require soldering basket wires to the device shaft and/or compacting the basket wires into a narrow diameter do not leave sufficient additional room for other devices within the narrow working channel. While the central lumen is useful for introducing instruments into the inner working area, alternative embodiments include filling the end of the cannula with solder or another material to form a tip that is less traumatic to tissue.
An additional advantage of the present invention is the relative simplicity of construction. Devices comprised of a metal cannula or cylinder can be formed by making a series of longitudinal slots through the cannula/cylinder to form individual resilient grasping members. The process results in perfectly aligned grasping members and, except for reforming the grasping members, eliminates much of the skilled hand work normally required to assemble a basket or grasper forceps. Plastic deformation or heat setting the resilient grasping members into the outwardly extending configuration of a basket or forceps advantageously removes bending stresses and puts the expanded device in a relaxed condition during deployment. Retrieval devices of the present invention can use an external constraining mechanism such as a coaxial outer sheath or endoscope to open and close the resilient grasping members which capture and retain the target object for removal from a patient. Alternative methods could include an actuating member disposed in the lumen of the device to open and close the basket or grasper forceps.
In another embodiment of the present invention, the retrieval device is formed from an elongated member comprising a plastic tube having reinforcement wire encased therein. These wires, each representing a continuum of material extending the length of the elongated member, are exposed within the distal portion of the tube that interconnects them, where they are then formed into the resilient grasping members for making a retrieval basket or grasping forceps.